Fish populations in the Green and Yampa rivers have undergone significant changes in the last century Today, more than 50 fish species can be found in these rivers, but fewer than a third of those are native to the Green and Yampa. Of the 14 native fish species, four are endangered--the razorback sucker, humpback chub, Colorado pikeminnow, and bonytail--and others are declining.
The Green and Yampa Rivers
Fish native to the Green and Yampa evolved in natural-flowing rivers whose water was often clouded by dirt, silt, and other sediments that washed in from the surrounding countryside; in rivers with high spring flows fed by snow melt; and in rivers where water temperatures could range from near freezing in winter to almost 70F (21C) in summer.
The Green River - After Flaming Gorge Dam
In 1962, with the construction of Flaming Gorge Dam, these conditions largely disappeared from the Green River. Spring flows, temperature fluctuation, and turbidity (the cloudiness of the water) were all reduced.
The Green River downstream from the dam became a much clearer, cooler, and calmer river. These changes reduced the number and distribution of several native fish, all of whom were adapted to the rugged conditions of the undammed Green River.
Many of these changes in the river system also created more favorable conditions for non-native fishes.